Method of manufacturing a unitary composite article comprised of a core and lining

ABSTRACT

A method of manufacturing a writing implement having an inner body portion of unfoamed resin. The method consists of inserting a heated probe into the inner body portion so as to cause the foamed resin to become molten, withdrawing the probe and simultaneously inserting a writing core into the cavity, and allowing the body to cool whereby foamed resin adheres and bonds to the writing core.

United States Patent inventor Bernard 1. Bar-tner 229-07 58th Ave.,Bayside, N.Y. 11364 Sept. 4, 1969 Dec. 7, 1971 Continuation-impart 01application Ser. No. 631,652, Apr. 18, 1967. Thk application Sept. 4,1969, Ser. No. 860,150

App]. No. Filed Patented METHOD OF MANUFACTURING A UNITARY COMPOSITEARTICLE COMPRISED OF A CORE AND LINING [56] References Cited UNITEDSTATES PATENTS 3,340,] 15 9/l967 Rubenstein 156/294 X 3,500,819 3/1970Silverman l56/294 X Primary Examiner-Carl D. Quarforth AssistantExaminerStephen J. Lechert, Jr Attorney-Jerome Bauer ABSTRACT: A methodof manufacturing a writing implement having an inner body portion ofunfoamed resin. The method consists of inserting a heated probe into theinner body portion so as to cause the foamed resin to become molten,withdrawing the probe and simultaneously inserting a writing core intothe cavity, and allowing the body to cool whereby foamed resin adheresand bonds to the writing core.

PATENTEI] DEC 7 I971 SHEET 1 OF 2 R E HN m N BA VB WI D R A N R E B BY iATTORNEY PATENTEDuEc 719?: 3625788 sum 2 OF 2 INVENTOR. BERNARD I.BARTNER ATTORNEY METHOD OF MANUFACTURING A UNITARY COMPOSITE ARTICLECOMPRISED OF A CORE AND LINING This application is acontinuation-in-part of my copending application Ser. No. 63 I,652,filed Apr. 18, I967.

BACKGROUND OF THE INVENTION The present invention relates to unitarycomposite articles, such as writing instruments and the like, andmethods of manufacturing such articles.

In the manufacture of a unitary composite article such as a lead pencil,it had been customary to provide a pair of complementary shapedelongated wooden members each of which is formed with a groove forreceiving part of a lead core. The lead core is received in the boreformed by the grooves of the pair of elongated wooden members which arethereafier joined to each other by a suitable adhesive or the like, sothat in this way lead pencils are conventionally manufactured. As aresult of these procedures, it is necessary to carry out a multiplicityof steps in order to manufacture lead pencils, undesirably increasingthe cost thereof, and because of problems encountered with respect tothe joining of the wooden bodies to each other and to the lead core, areliable bond between these components is not always achieved.

SUMMARY OF THE INVENTION It is accordingly a primary object of thepresent invention to provide a unitary composite article and method ofmanufacturing the same which will avoid the aforementioned problems.

In particular, it is an object of the present invention to provide aunitary composite article such as a writing instrument that may take theform of a crayon pencil or lead pencil which obviates the cumbersomeprior art practice of joining separate casing components to each othersurrounding the core of the writing instrument and the use of a bondingadhesive therebetween.

In particular, it is an object of the invention to provide a unitarycomposite article where an inner elongated member is encased within aone-piece exterior casing so that the problems encountered with theconventional constructions can be avoided.

Further, it is an object of the present invention to provide a methodaccording to which an elongated member, such as a marking or writingmember, as the core of a lead pencil, is in troduced into the interiorof a one-piece body which encases the core or elongated member whilealso becoming firmly bonded thereto, so that it becomes possible withthe method of the invention to manufacture articles such as writinginstruments or the like at a far lower cost than conventional articlesof this type while at the same time eliminating the problems encounteredwith the finished article, such as the reliable holding together oradhesion of the components thereof.

In accordance with the method of the invention, an elongated member isintroduced to the interior of an elongated body of a foam thermoplasticwhile the body is in a plastic condition. By the method of theinvention, the elongated member directly engages the inner surface ofthe elongated body so that during subsequent cooling and setting of thebody, its inner surface becomes securely and permanently bonded with theelongated member, thereby resulting in the unitary composite article.The elongated body of foam thermoplastic can be extruded in aconventional manner and an elongated heated probe may be axially passedthrough the body of foam plastic for providing it with its heated innersurface which subsequently engages the elongated member. This lattermember may be introduced into the plastic body substantiallysimultaneously with withdrawal of the probe therefrom. The heated probehas been used to form a bore in the body the dimension of which isdetermined by the size of the outer surface of the probe. However, ithas been found that the body may be initially extruded with a bore sothat when the probe is introduced into the bore the surface whichdefines the bore will become heated, softened and plastic. The elongatedmember itself may have a diameter slightly greater than that of theinner surface of the bore which is in the heated plastic condition, sothat this bore becomes expanded slightly during the introductionthereinto of the elongated member and thus forms a secure bondtherewith. During its extrusion, the plastic body is provided at itsouter surface with a nonfoamed plastic at least partially covering theouter surface of the plastic body, so thatthe rigidity of the body isincreased without adversely affecting its machine-abilitycharacteristics. Thus, it becomes possible to machine the resultingunitary composite article in a conventional pencil sharpener.

The foamed inner body may have two foamed concentric layers, with theouter layer having been foamed in the extruder and the inner layersubsequently foamed in situ as a consequence of contact with the heatedprobe.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated by way ofexample in the accompanying drawings-which form part of this applicationand in which:

FIG. I is a schematic illustration of one possible manner in whichelongated plastic bodies may be formed;

FIG. 2 is a transverse section, taken along line 22 of FIG. 5 in thedirection of the arrows, of a plastic body extruded with the structureof FIG. I; I

FIG. 3 is a transverse section of the plastic body taken along line 3-3of FIG. 7, in the direction of the arrows;

FIG. 4 is a schematic side elevation, partly in longitudinal section, ofan enlarged heating structure used in the method of the invention;

FIG. 5 illustrates on stage in the manufacture of an article accordingto the method of the invention;

FIG. 6 shows a stage in the method subsequent to that of FIG. 5;

FIG. 7 illustrates a stage in the method of manufacture of the inventionsubsequent to that of FIG. 6;

FIG. 8 shows, in side elevation, one possible article of the presentinvention manufactured according to the method of the invention;

FIG. 9 is a schematic illustration of a manner of forming anotherembodiment of the elongated plastic bodies of this invention;

FIG. I0 is a transverse section, taken along line l0-10 of FIG. 9 in thedirection of the arrows, of a plastic body extruded with the structureof FIG. 9;

FIG. 11 illustrates one stage in the manufacture of an article accordingto the method of the invention; and

FIG. 12 illustrates a stage in the method of manufacture of theinvention subsequent to that of FIG. I 1.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, andfirst to FIGS. 1-8, with initial reference to FIG. 8, the unitarycomposite article, generally identified by the numeral 10, isillustrated therein as a lead or a coloring pencil, having a writingcore I2 which at one end projects beyond a casing or body 14 whichsurrounds the core I2. The core 12 thus forms an elongated membercapable of making a mark on paper so that the article 10 may be said tobe a writing instrument. The casing generally identified by the numeral14 encases the elongated core member 12 and has, in the illustratedsample, an outer shell 16 of a relatively rigid nonfoamed plastic. Thisshell 16 of the elongated body 14 surrounds and is integrally extrudedwith a foam plastic inner lining or portion 18 which extendslongitudinally through and for the length of the shell 16. The plasticbody 14 is made of any suitable thermoplastic, as referred to in greaterdetail below. It is a one-piece body which finnly adheres and ispermanently bonded at its inner surface to the exterior surface of theelongated member 12, the result of which is an inseparable unitarycomposite structure.

The cellular structure of the foam plastic inner lining 18 approximatethe structure and characteristic of wood, thereby enabling it to bemachined with the same ease as wood in a conventional pencil sharpener.If the whole body 14 were of such porous or cellular structure as theinner lining 18, it would be too flexible and, therefore, it would notsufiiciently protect the soft core 12 therewithin. Hence, the addedprotection of the harder, less porous and more rigid outer shell 16.When this thin outer shell 16 is applied to the inner lining 18, it addssufficient rigidity to the body that limits flexing or bending of thebody that might damage its inner core 12.

In order to manufacture the article 10, in accordance with the method ofthe invention, the body 14 thereof is extruded in a conventionalextruder 20 shown in FIG. l.This extruder contains the foam plastic mass22 which is urged outwardly through the extruder outlet 24 in anysuitable way, such as by a plunger or piston 26 which is acted upon in aconventional manner. If desired, a screw-type of material feeder can beprovided for the extruder to urge the plasticized mass 22 out of thelatter. This mass 22 is a thermoplastic material which contains asuitable foaming agent so that the resultant extrusion will be composedprimarily of a foamed plastic porous in structure and having amultiplicity of cells therein which may be either of the open or closedtype.

Positioned about and in the region of the outlet 24, the extruder 20 hasan annular chamber 28. The chamber 28 surrounds the outlet opening 24through which the mass 22 issues and communicates with a mass ofnonfoamed plastic 30 which is compatible with the material 22 so as toform an integral and indistinguishable body therewith. Because thechannel 28 surrounds the outlet 24 through which the extruded mass 22issues, the material 30 forms the outer shell covering 16 of the body14. It is this nonfoamed plastic coating 16 that gives the cellularfoamed body 18 added rigidity. The mass of plasticized nonfoamedmaterial 30 is urged out of the chamber 32 by a plunger 34 acted upon ina conventional way, or in this case also a screw-type of material feedermay be used.

If desired, the channel 28 need not form a continuous circle around thebore through which the material 22 issued, and instead it can beinterrupted by ribs extending across the channel 28 in the direction ofthe axis of the outlet 24 through which the material 22 issues. Theseribs may be uniformly or nonuniformly distributed about the axis of thechannel 28 to interrupt the flow and extrusion of the material 30 aboutthe prior extruded material 22. By controlling the design of the ribbingof the outlet channel 28, it has been found possible to applyreinforcing rigidifying ribs to the extruded material 22 rather than toapply a full and complete shell covering 16. In this way it is alsopossible to achieve many different types of decorative effects on theouter surface of the body 14.

Thus, it will be recognized that as the foam plastic material 22 isextruded through the outlet 24, its outer cellular surface is almostimmediately impregnated with the nonfoaming plastic material 30. As thematerial 30 is extruded, it flows into the porous, cellular structure ofthe material 22, fusing therewith and becoming indivisible andinseparable therefrom. For all purposes, the two materials 22 and 30become one whole, unitary extruded body. The inner portion or lining 22becomes the part in the article identified as the lining 18, while theouter covering 30 is the shell 16.

Upon issuing from the extruder 20, the composite extrusion passesthrough a cooling bath 36 of any conventional construction, and istransported by means 38, which may be driven in any suitable way, to acutter unit 40, also of any conventional construction. This unit 40 cutsthe extruded rod into bodies 14, of preselected lengths, collected inany suitable receptacle, as schematically indicated at the lower rightportion of FIG. 1. The extruded bodies will have in cross section theconstruction indicated in FIG. 2 which illustrates the inner cellularbody 18 of foam thermoplastic surrounded by the indivisibly andintegrally fused outer shell 16 of nonfoamed plastic that is polymerizedtherewith.

After each body 14 is formed it is worked upon by a heated probe 42indicated in FIG. 4. This probe may take the form, for example, of anichrome wire 44 encased within a suitable casing 46 with an end 48 ofthe wire 44 exposed and electrically joined, as by silver solder 50 toan outer stainless steel casing 52. This casing 52 and the wire 44 areelectrically connected with a pair of conductors of a lead 54 joined toany power source 56, so that when the latter is energized the probe 42will be heated.

Referring now to FIG. 5, the body 14 and the probe 42 are initiallysituated at opposite ends of the body 14 and with respect to each othersubstantially in the manner shown in FIG. 5. While the body 14 is heldin any suitable holding structure (not shown), the heated probe 42 isguided into and through the body 14 so that the outer shell 52 of theprobe, which is at an elevated temperature, pierces at its leadingpointed end the body 14 to produce or form an axial hollow or boretherein. During the time the probe 42 pierces through the body 14 toform the latter with an axial bore, the elongated member 12, in the formof a lead core in the illustrated example, is maintained in readiness ofany suitable support to be pushed into the body 14 at its opposite end.

In the event the body 14 is extruded as a solid rod, as shown in crosssection in FIG. 2, it will be necessary to form the same by the probe 42with a central axial bore 43 therethrough to enable it to subsequentlyreceive the member 12 therein. On the other hand, it has been foundconvenient to initially extrude the body 14 with a central hollow oraxial bore 43 as in FIG. 3. If the bore 43 is initially extrudedtherein, its size will be smaller than that of the heated probe 42which, in turn, is smaller than that of the insert 12. Thus, while thebody 14 is held in any suitable holder (not shown) the heated probe 42will enter the bore 43 to be guided thereby to penetrate the length ofthe body. As the heated probe 42 quickly penetrates the length of thebore 43 or forms the same, the cellular lining l8 breaks down and meltsrapidly under its heat, thereby enlarging the bore size. Hence, it isimportant that the operation of the probe be performed rapidly. Itsinsertion into and removal from the body 14 should be no longer than isnecessary to form the bore 43 of the size opening that is justsufficient to accommodate the receipt of the insert member 12 therein.If the probe 42 remains in the body too long, its heat will form anincreasingly larger bore by causing the adjacent cellular structure ofthe lining 18 to melt and break down. Thus, to facilitate the rapid andalso accurate insertion of the probe 42 into the body, it is convenientif the body is initially extruded with the bore 43. The terms melt,melts" and "molten" herein refer to a heated condition of the foamedthermoplastic material sufficient to cause material flow under theprevailing conditions of heat and pressure. Molten or melt or meltsstate is often referred to as being plastic.

Consequently, it will be clear that the heated probe 42 will form thecentral bore 43 if none previously existed, or if one was thereinitially, it will enlarge the same. The longer it remains in the bore43, more cells of the foam lining will be melted and, therefore, thelarger will be the resultant bore 43. For this reason, it is a goodpractice to attempt to insert the core 12 into the body bore 43 almostsimultaneously or as soon as possible after the removal of the probe 42after it has reached its end position of FIG. 6. Therefore,substantially simultaneously with the removal of the probe 42 from thebore 43, and while the inner surface of the bore is still in its moltenstate, the core 12 is forced thereinto as shown in FIG. 7. This may beaccomplished by the use of any desired pusher structure 58.

As the core 12 is forced into the bore 43 formed by the probe 42, itdisturbs the molten cellular structure of the foam plastic in which thebore exists. This results in surface to surface contact and engagementbetween the outer surface of the core 12 and the bordering cells of thebore 43. If the insertion of the core 12 is performed while the foamthermoplastic is in its heated plastic condition, the engaging cellularsurfaces of the bore adheres and becomes securely and permanently bondedto the core 12 as the thermoplastic hardens and sets.

, Furthermore, if the plastic is sufficiently molten when the core isinserted, the plastic will flow into whatever cells, pores or crevicesmay be present in the core so as to form a locking bond therewith. Theresultant structure is a core so permanently bonded to the interior ofthe body that they form a unitary combined article.

As has been indicated above, the body 14 is composed primarily of a foamthermoplastic material. As a result, when the inner surface of the bodyis heated and placed in a plastic condition, cells of the body break andflow so that the material of the body 14 spreads and flows along theexterior surface of the elongated member 12. During heating and settingof the body 14 at its inner surface it forms with the exterior surfaceof the member 12 a bond which has proved to be of the greatest strength,a highly intimate and secure connection being provided in this way. Itis to be noted that in dealing with a lead core 12, in particular,because of the slippery, somewhat greasy nature of this lead core,problems have been encountered in the prior art in joining the halfcasings of a wood pencil to such lead cores, whereas with the structureof this invention, without the use of any adhesive, solvent, or thelike, the inner surface of the body 14 directly adheres and permanentlybonds to the exterior surface of the member 12, forming an exceedinglysecure connection therewith in a very simple way.

The foaming of the plastic body 14 is achieved by the use of a foamingagent, as is well known in the art. In accordance with a further featureof the invention, this foaming agent may be activated when the innersurface of the bore 43 of the body 14 is heated and engages the exteriorsurface of the member 12. As a result of the heat derived from theheated inner surface of the bore 43 of the plastic body, the foamingagent continues to function and tends to expand the cells of the bodyinward toward the core 12 so that not only does it press the plasticcells into tighter frictional engagement and connection with the member12, but it mechanically grips and squeezes the member 12, thusincreasing the security of the adhesion and bond of the connection.

Another embodiment of the invention is illustrated in FIGS. 9-11depicting the manufacture of a composite article having the inner core12 surrounded by an inwardly directed foam cylindrical body 86 (See FIG.12). Cylindrical body 86 is encased within and integral withintermediate foam cylindrical body 62 which is surrounded by nonfoamshell 60. Shell 60 and intermediate body 62 correspond to shell 16 andbody 14 respectively.

The composite article illustrated in FIG. 12, in the last stages ofbeing manufactured, is first an extrusion product of extruder 66. Thisextruder 66 contains the nonfoam plastic mass C in the chamber 68. Theplastic mass C is urged outwardly by plunger 70 through the innerannular chamber 72 about the tube 73 to form an inner cylindricalnonfoam body 64 which is extruded with an inner bore 65, that may bemaintained open by a gas discharged thereinto by way of the tube 73.Chamber 74 contains foam plastic mass B. The foam plastic mass B isurged outwardly by plunger 76 through the intermediate annular chamber78 to form the intermediate foam cylindrical body 62. The chamber 80contains nonfoam plastic mass A. Plastic mass A is urged outwardly byplunger 82 through the outer annular chamber 84 to form the nonfoamshell 60.

Nonfoam shell 60 and intermediate foam body 62 are integral in the samefashion as described hereinbefore in connection with shell 16 and body14. Similarly, the inner nonfoam cylindrical body 64 is also integralwith the intermediate foam body 62.

The composite extrusion illustrated in FIG. is cut into segments ofspecified length and then worked upon by a heated probe 52 as indicatedin FIG. 11. The point of the heated probe 52 is inserted through thelength of bore 65. Mass C which forms the inner nonfoam cylindrical body64 is a thermoplastic material containing a foaming agent which does notdecompose or vaporize at the extrusion temperatures for mass C existentin extruder 66. The surface 52 of the probe is heated to a temperaturehigher than the extrusion temperature in extruder 66 and sufficientlyhigh to decompose or otherwise vaporize the foaming agent in body 64.This causes a foaming reaction and transfonns tenaciously body 64 intoinner foam cylindrical body 86. The foaming reaction causes an expansionin the mass of body 64 as it transforms and expands into foam body 86.As probe 52 is withdrawn, this expansion tends to be inward in thedirection of the axis of the cylindrical body. The core 12 is insertedinto the composite body as probe 52 is withdrawn, as illustrated in FIG.12, substantially simultaneously therewith and is tenaciously engaged byhot foam body 84.

The preparation of composite articles such as that illustrated in FIG.8, in accordance with the process schematically illustrated in FIG. 1,follows:

Polystyrene having a density of about 10 lbs. per cubic foot was usedfor body 14 and outer shell 6. The polystyrene=used to form the innercore member 12 was admixed with a foaming agent such as dichloroethanewhich vaporizes at a temperature of about Il90 F. The polystyrene usedfor the outer shell 16 did not contain a foaming agent. Bothpolystyrenes were heated and extruded at a temperature of about 325 F.An elongated heated probe having a surface temperature of about 500 F.was inserted through the body 14 to form the latter with an axial bore.The elongated probe was then removed while concomitantly inserting theelongated member 12 from the opposite end of the body 14 which had beenpierced.

The production of the composite article illustrated in FIGS. 9-12 inintermediate stages of manufacture follows:

The outer shell 60 and the intermediate foam body 62 correspond to theouter shell 16 and the body 14 described in the preceding paragraph. Thesame polystyrene materials are used. The inner nonfoam body 64 is alsoprepared from a nonfoam polystyrene having a density of about 10 lbs.per cubic foot. This material (plastic mass C) contains a foaming agentwhich does not decompose under the conditions present in the extruderbut which will decompose at a higher temperature. Polystyrene admixedwith an azobisforrnamide (decomposition temperature 360-400 F.) wasadmixed with the polystyrene. All the extrusions were at a temperatureof about 300 F. The extrusion formed a'stiff composite materialcontaining a nonfoam outer shell 60, an intermediate foam body 62 and aninner nonfoam shell 64 surrounding a central bore 65. The elongatedheated probe 52 is then inserted into and through bore 65. The elongatedheated probe 52 was at a temperature of 500-600 F. and caused the innerbody 64 to foam and expand into foam body 86. The elongated probe 52 wasthen withdrawn while concomitantly inserting the elongated core 12 asillustrated in FIG. 12 from the opposite side. The expansion resultantfrom the foaming reaction together with the effect of heat at theinterface of the body 86 and the core 12 caused an adherent bond.Although the outer shell 60, the intermediate foam body 62, and theinner foam body 86 are referred to herein separately, it is to beunderstood that by virtue of their formation as a common extrusion thethree shells form an integral composite. The integrity of the compositeis illustrated by the difficulty in delineating a sharp boundary betweenadjacent bodies 60-62 or 62-86 when the completed product is crosssectioned.

The composites of this invention have been made of numerousthermoplastics. Thus, polystyrene with a suitable foaming agent has beensuccessfully used for the inner foam portions 18, 62 and 64 whilenonfoamed polystyrene is used for the outer shells I6 and 60, althoughany other compatible plastic which is not foamed could also be used forthis purpose. In addition, polypropylene has been used with a suitablefoaming agent for the interior portions 18 and 62, while nonfoamedpolypropylene is used for the outer shells l6 and 60. Polystyrene; highimpact polystyrene, i.e., rubber modified polystyrene such aspoIybutadiene-styrene (e.g., 5-15 percent butadiene); polypropylene; andrigid polyvinylchloride are the preferred thermoplastic resinousmaterials. Other resinous thermoplastics are generally less preferredbecause of their higher cost. These include the cellulosics, theacrylonitrile-butadiene-styrenes, the acrylic resins such asmethacrylate, polyethylene and the polyamids, e.g., nylon. Allthermoplastic materials, which may be hardened to a degree of rigiditycompatible with the intended use and which may be extruded and foamed ofwhich the aforespecified are illustrative, may be used. Although thedifierent cylindrical shells for bodies may be formed of differentthermoplastic materials, it is preferred that-they be of the samematerial. This preference follows from the ability to utilize such scrapfrom the process as a raw 1 material.

The foaming agents utilized are the conventional foaming agents whichdecompose or vaporize at the process condition specified. These includeinorganic carbonates, such as sodium bicarbonate; alkanes such aspentane and hexane; halogenated alkanes such dichloroethane; aromaticssuch as benzene; ethers such as the aliphatic and petroleum ethers, etc.These are illustrative of foaming agents having decompositiontemperatures below about 300 F. Foaming agents having higherdecomposition or vaporization temperatures are particularly useful forfoaming in situ after extrusion, such as the azonitriles such asazobisformamide. Suitable foaming agents are readily selected from thoselisted in conventional references as on pages 380 to 387 of ModernPlastics Encyclopedia, 1968-4969 Edition, published by McGraw-HillIncorporated, New York, N.Y. The foam mixture in the extruder may alsobe formed by direct injection of gas, e.g., nitrogen or pentane, at atemperature of about 100 F. into chambers 22 and 74.

The density of the thermoplastic used for the foamed portion or portionsof the body can be varied. In the case of polystyrene, it has been foundthat this density may range from the neighborhood of 6 pounds per cubicfoot up to approximately 16 pounds per cubic foot. The particular choicewill depend on the results which are to be achieved. For example, solidpolystyrene is far too brittle to be machined in a conventional pencilsharpener and will tend to shatter, creating considerable difficultiesin the sharpening. However, at relatively low densities, lower thanapproximately 6 pounds per cubic foot, the foamed inner portion of thebody 10 becomes much too flexible, while at densities greater than 16pounds per cubic foot it becomes too tough. By reason of the outer shell16, or at least by reason of partially covering the foam portion with anouter portion of nonfoamed plastic, it is possible to provide a veryeasily machinable body, capable of being handled without any difficultywhatsoever in a conventional pencil sharpener, at the same timeproviding the body with the required rigidity. The same considerationswill, of course, apply to any thermoplastic, and depending upon thedesired properties of the final unitary composite article, it ispossible to choose suitable densities and a suitable extent of foaming.

While the above-described method and article of the invention refer to alead pencil, the invention is applicable to many other types ofarticles. Many different types of elongated members can be encasedwithin the body 14 or 86 according to the method of the invention. Forexample, instead of black lead, the elongated core member 12 may takethe form of crayon of any desired color. The elongated member 12 mayalso form a ballpoint pen filler which is enclosed at its exteriorsurface within the plastic body and with the writing end of the penprojecting beyond the plastic body.

During the practice of the invention, it has been found that instead ofusing a heated probe 42 (52), it is possible to heat the elongated coremember 12 just prior to insertion thereof into the body 14, so that thiscore member 12 itself will form its own conforming bore. in the casewhere the body is extruded with a preformed axial bore insert 43 or 65,it will serve as guide for the rapid insertion of the heated core 12thereby assuring its exact central location within the body. During suchinsertion, the heated core member 12 will heat the adjacent cells of thethermoplastic material to a molten condition. As the heat dissipates,the plastic hardens and firmly adheres and bonds to the surrounded wallof the core member.

One of the advantages achieved by using the foam form of the elongatedbody is that the thermoplastic material can be used to a far greaterextent for a greater number of articles because of the lesser amount ofthe thermoplastic used for any one article. Furthermore, when using foamplastics, there are limitations on the coloring which may be providedfor the article, since it is difficult to obtain dark shades for foamplastics. Also, the feel of the article is not as comfortable as thetactile qualities of a solid nonfoamed plastic. Thus, by providing anouter shell 16, or at least a partial exterior covering of a nonfoamedplastic, it becomes possible to produce an article which is morecomfortable to handle and which can be provided in a far easier mannerwith any desired coloration or even with any desired printed matter,advertising matter, or the like.

Thus, with the method of the invention, it is possible to produceunitary combined articles of the invention which have a very pleasingexterior appearance and which are pleasant to handle while at the sametime, in the case of lead pencils, being easy to machine. The colorationcan take many different forms, including swirls of different colors andwhen using elongated striations of solid nonfoamed plastic at theexterior of the body, extending longitudinally thereof, leaving portionsof the foam plastic uncovered, particularly pleasing effects have beenachieved. One of the further advantages which is derived from the use ofan outer nonfoamed plastic is that the tendency of the foamed plastic tohave an exterior surface which is formed with longitudinal scratches orgrooves as it issues from the extruder is avoided because the nonfoamedplastic gives to the exterior of the article a smooth outer surfacewhich is free of such defects. The use of the outer, harder shell 16 ofnonfoamed plastic limits the extent to which the body 10 can be bent, sothat in this way the inner core member 12 is protected. Without anouter, at least partial, covering of nonfoamed plastic, the flexiblefoam will permit easy bending of the article, which may be desirable insome uses but will result in breaking a brittle core 12 when the lattertakes the form of the lead of a lead pencil.

While there have been shown and described and pointed out thefundamental novel features of the invention as applied to a preferredembodiment thereof, it will be understood that the various omissions andsubstitutions and changes in the form and details of the deviceillustrated and in its operation may be made by those skilled in theart, without departing from the spirit of the invention. lt is theintention, therefore, to be limited only as indicated by the scope ofthe claims appended hereto.

What is claimed is:

1. ln a method of manufacturing a writing implement having a bodyportion of foamed thermoplastic resinous material provided with an outerlining of unfoamed resin selected from the group consisting ofpolystyrene, polypropylene, polyethylene and rigid polyvinylchloride andthe body portion of foamed resin selected from the group consisting ofpolystyrene, polypropylene, polyethylene and rigid polyvinylchloride,said method comprising inserting a heated probe into the body portion soas to cause the foamed thermoplastic in the area about the probe tobecome molten and to form a core receiving cavity, withdrawing theheated probe and simultaneously inserting a writing core into thecavity, and allowing the body to cool whereby the foamed thermoplasticportion adheres and bonds firmly to the writing core.

2. In a method of manufacturing a unitary composite article having abody of foam thermoplastic resinous material and a core, the stepscomprising making the body with a lining of foam thermoplastic material,inserting the core into the lining of thermoplastic material while atleast a portion of the lining is in a plastic condition, by treating theportion of the lining of the thermoplastic material into which the coreis inserted to place the lining in its plastic condition while the coreis inserted thereinto, so that upon subsequent changing of the liningfrom its plastic to its set condition, it engages said body to form aunitary composite article.

3. In a method of manufacturing an elongated unitary composite articleof a core member and a preformed plastic body in which the interior ofthe plastic body has a foam thermoplastic material lining of cellularstructure that melts and breaks down rapidly under heat, the stepscomprising inserting the core member into the interior of the cellularlining of foam thermoplastic material while such material is in a heatedmolten condition, so that the core engages the plastic material whilethe same is in its heated molten condition, allowing the plasticmaterial to cool and upon the cooling and setting of the material, thesame adheres to the core to bond the body and core together to form theunitary composite article.

4. In a method as recited in claim 3,

the steps of inserting a heated probe into said cellular lining prior toinsertion of said core member into the cellular lining to provide saidcellular lining with a heated inner surface which is in moltencondition, withdrawing said probe from said cellular lining while saidinner surface thereof is in said molten condition, and inserting saidcore member into said cellular lining into engagement with said heatedinner surface thereof substantially immediately upon withdrawal of saidprobe from said cellular lining so that said cellular lining will havesaid inner surface thereof still in said molten condition to engage saidexterior surface of said member and become joined thereto upon coolingand setting of said cellular lining at said inner surface thereof.

5. In a method as recited in claim 4,

wherein said cellular lining is elongated and said probe is directedlongitudinally through said elongated cellular lining from one end tothe other end thereof so that said heated surface of said cellularlining defines an axial bore passing therethrough,

and introducing said core member into said cellular lining from saidother end toward said one end thereof substantially simultaneously withthe withdrawal of said probe from said cellular lining through said oneend thereof so that as said probe is displaced out of said cellularlining said core member is substantially simultaneously introduced intothe latter to engage said inner surface while the latter is still in aheated molten condition.

6. In a method as recited in claim 4, wherein said resinousthermoplastic material is at least one material selected from the groupconsisting of polystyrene, high impact polystyrene, polypropylene andrigid polyvinylchloride.

7. In a method of manufacturing an elongated unitary composite articleof a core member and a preformed thermoplastic resinous body, the stepscomprising forming an elongated composite having a cylindrical foamthermoplastic resinous body surrounding an inner axially hollowcylindrical nonfoam thennoplastic resinous body containing admixedtherewith a foaming agent, heating said inner nonfoam body to atemperature sufficient to cause a foaming reaction whereby said innernonfoam body is transformed into a cellular body and inserting the coremember into the axial hollow whereby it is tight bonded to said cellularbody.

8. In a method as recited in claim 7, wherein said probe is withdrawnwhile said inner surface is in a molten condition, and inserting saidcore member into said body into engagement with the inner surfacethereof substantially immediately upon withdrawal of said probe fromsaid body.

9. In a method as recited in claim 8, wherein said resinousthemioplastic material is at least one material selected from the groupconsisting of polystyrene, high impact polystyrene, polypropylene, rigidpolyvinylchloride and polyethylene.

10. In a method of manufacturing a writing implement having a bodyportion of foamed thermoplastic resinous material provided with an outerlining of unfoamed resin selected from the rou consistin of ol st rene,l ro lene, polye iyle e and rigid golyvinyl hlbride and th bzii iy grtion of foamed resin selected from the group consisting of polystyrene,polypropylene, polethylene and rigid polyvinylchloride and in which saidbody portion has an axial bore, said method comprising inserting a corehaving a dimension larger than said axial bore in a heated conditioninto said axial bore to form an enlarged bore therein to the size andshape of said core, allowing the core and body to cool so that aftersaid core and body cool and said body sets, its inner surface willadhere to and be joined with said core. I

2. In a method of manufacturing a unitary composite article having abody of foam thermoplastic resinous material and a core, the stepscomprising making the body with a lining of foam thermoplastic material,inserting the core into the lining of thermoplastic material while atleast a portion of the lining is in a plastic condition, by treating theportion of the lining of the thermoplastic material into which the coreis inserted to place the lining in its plastic condition while the coreis inserted thereinto, so that upon subsequent changing of the liningfrom its plastic to its set condition, it engages said body to form aunitary composite article.
 3. In a method of manufacturing an elongatedunitary composite article of a core member and a preformed plastic bodyin which the interior of the plastic body has a foam thermoplasticmaterial lining of cellular structure that melts and breaks down rapidlyunder heat, the steps comprising inserting the core member into theinterior of the cellular lining of foam thermoplastic material whilesuch material is in a heated molten condition, so that the core engagesthe plastic material while the same is in its heated molten condition,allowing the plastic material to cool and upon the cooling and settingof the material, the same adheres to the core to bond the body and coretogether to form the unitary composite article.
 4. In a method asrecited in claim 3, the steps of inserting a heated probe into saidcellular lining prior to insertion of said core member into the cellularlining to provide said cellular lining with a heated inner surface whichis in molten condition, withdrawing said probe from said cellular liningwhile said inner surface thereof is in said molten condition, andinserting said core member into said cellular lining into engagementwith said heated inner surface thereof substantially Immediately uponwithdrawal of said probe from said cellular lining so that said cellularlining will have said inner surface thereof still in said moltencondition to engage said exterior surface of said member and becomejoined thereto upon cooling and setting of said cellular lining at saidinner surface thereof.
 5. In a method as recited in claim 4, whereinsaid cellular lining is elongated and said probe is directedlongitudinally through said elongated cellular lining from one end tothe other end thereof so that said heated surface of said cellularlining defines an axial bore passing therethrough, and introducing saidcore member into said cellular lining from said other end toward saidone end thereof substantially simultaneously with the withdrawal of saidprobe from said cellular lining through said one end thereof so that assaid probe is displaced out of said cellular lining said core member issubstantially simultaneously introduced into the latter to engage saidinner surface while the latter is still in a heated molten condition. 6.In a method as recited in claim 4, wherein said resinous thermoplasticmaterial is at least one material selected from the group consisting ofpolystyrene, high impact polystyrene, polypropylene and rigidpolyvinylchloride.
 7. In a method of manufacturing an elongated unitarycomposite article of a core member and a preformed thermoplasticresinous body, the steps comprising forming an elongated compositehaving a cylindrical foam thermoplastic resinous body surrounding aninner axially hollow cylindrical nonfoam thermoplastic resinous bodycontaining admixed therewith a foaming agent, heating said inner nonfoambody to a temperature sufficient to cause a foaming reaction wherebysaid inner nonfoam body is transformed into a cellular body andinserting the core member into the axial hollow whereby it is tightbonded to said cellular body.
 8. In a method as recited in claim 7,wherein said probe is withdrawn while said inner surface is in a moltencondition, and inserting said core member into said body into engagementwith the inner surface thereof substantially immediately upon withdrawalof said probe from said body.
 9. In a method as recited in claim 8,wherein said resinous thermoplastic material is at least one materialselected from the group consisting of polystyrene, high impactpolystyrene, polypropylene, rigid polyvinylchloride and polyethylene.10. In a method of manufacturing a writing implement having a bodyportion of foamed thermoplastic resinous material provided with an outerlining of unfoamed resin selected from the group consisting ofpolystyrene, polypropylene, polyethylene and rigid polyvinylchloride andthe body portion of foamed resin selected from the group consisting ofpolystyrene, polypropylene, polethylene and rigid polyvinylchloride andin which said body portion has an axial bore, said method comprisinginserting a core having a dimension larger than said axial bore in aheated condition into said axial bore to form an enlarged bore thereinto the size and shape of said core, allowing the core and body to coolso that after said core and body cool and said body sets, its innersurface will adhere to and be joined with said core.